Steve Souders has done extensive research on improving front-end performance of website. He has shared his findings on "domain sharding":
- Most of the U.S. top ten web sites do domain sharding.
- The optimal number of domains to shard across is 2-4. After 4 domains, response time degrades
- Domain sharding is especially useful for older browsers as they are restricted to just two parallel downloads per hostname. The newer browsers however do better. Opera 9+ and Safari 3+ do four downloads per hostname. Internet Explorer 8, Firefox 3, and Chrome 1+ do six downloads per hostname.
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